Preservation of the viability of cells in an organ or tissue during transplantation is problematic. The probability that a tissue will survive the process of transplantation depends on many factors including the status of the tissue prior to removal, the duration of time that the tissue remains outside the body and the procedure utilized to initiate reperfusion of the tissue in the recipient.
One source of injury that affects the success of tissue and organ transplantation is oxygen deprivation. In jury of organs, tissues, and cells occurs when the regular flow of oxygenated blood to the tissue and cells is interrupted. This occurs during surgical procedures to remove the organ from a living or recently deceased donor and subsequently during storage ex vivo prior to transplantation into a recipient. However, the most problematic stage in the transplantation process is the grafting of tissue into the recipient and reperfusion of the grafted tissue with oxygenated blood. When reperfusion occurs and energy metabolism starts up again, free radicals accumulate in the cells where anti-oxidant capacity has been diminished. The accumulation of free radicals contributes to post-transplantation injury in tissue giving rise to an increased number of damaged cells and an enhanced immune response by the recipient host. The immune response to transplanted cells includes inflammation caused by cellular antigens exposed by the damaged implanted cells.
Current attempts to reduce damage to tissues during transplantation rely on two general approaches. These are: 1) cooling the tissue to slow metabolic rate; and 2) minimizing the time between removal of the organ or the tissue from the donor and implantation of the tissue or organ into the recipient. During the time in which the body part is readied for transplantation, it is maintained in an isotonic solution. In addition, various investigators have explored the effect of adding anti-oxidants to cells and tissues in isotonic solution prior to implantation into a recipient. These antioxidants include alpha tocopherol (vitamin E), normally found in plasma membranes and membranes of the mitochondria and found to positively impact graft survival (Demirbas et al., Transplantation Proceetlings (1993) 25:2274; Ikeda et al. (1996) Life Sciences 59:781-8; Laue et al. (1995) Tranvsplantation Proceediings: 1875-6;); a compound (EPC-K1), a phosphodiester linkage between vitamin E and vitamin C (Tanemoto et al., Acta-Med-Okayama (1993) 47:121-7); 2-mercapto-imidazole derivatives (Chaudiere et al., WO 9,5 1 8,108); alpha keto-glutarate containing infusible compounds (Ekroth et al., WO 9,534,301); amino acids (Kramer et al., WO 9519768); creatine analogs (Elgebaly et al., WO 9,426,261); and ginkgolide (Ramwell et al., U.S. Pat. No. 5,002,965). In addition, monitoring of isotonic conditions has been found useful in reducing adverse effects on transplanted tissues. (Martindale et al., U.S. Pat. No. 5051352). In studies on the fate of transplant tissue after insertion into the recipient, Foegh et al. (1995) (Journal of Heart and Lung Transplantation (1995) vol. 14, p. S170) reported that estrogen attenuated transplant atherosclerosis by inhibiting abnormal cell growth of smooth muscle under transplant conditions.
There is a need for methods to improve the viability of cells removed from a donor, maintained outside of the body, and implanted into a recipient, such that cell damage is minimized thereby increasing the likelihood of a successful graft through improved viability of the cells and reduced problems resulting from adverse immune reactions.